Example: When opening a non-existent file:

>>open("abc.txt","r")
Will prompt errors

Traceback (most recent call last):
File "D:/project1/test.py", line 11, in <module>
open("abc.txt","r")
FileNotFoundError: [Errno 2] No such file or directory: 'abc.txt'

This exception can then be caught and handled with try....except statement

try:
    open("abc.txt","r")
except FileNotFoundError:
    print("Error")
----------------------
At this point, the operation will only print "Error"

If the statement is replaced by:

try:
    print(a)
except FileNotFoundError:
    print("Error")
----------------------

Traceback (most recent call last):
File "D:/project1/test.py", line 12, in <module>
print(a)
NameError: name 'a' is not defined

At this time, because "FileNotFoundError" means an error when a file cannot be found, which is not consistent with the current "NameError", the code can be changed to the following:

try:
    print(a)
except NameError:
    print("Error")

However, in Python, all exceptions are inherited from Exception. Since version 2.5, a new base class BaseException has emerged, and the new base class can accept all exceptions:

try:
    print(a)
    open("abc.txt","r")
except BaseException:
    print("Error")
-------------------------
No matter which line is abnormal, we can catch and print "Error" but we can't know which line is wrong. At this time, we can print the abnormal information:

try:
    print(a)
    open("abc.txt","r")
except BaseException as msg:
　　print(msg)
　　print("Error")
-------------------------
[Errno 2] No such file or directory: 'abc.txt'

The following are common exceptions in Python:

The use of exceptions combined with else:

try:
    a ="Exception testing:"
    print(a)
except NameError as msg:
    print(msg)
esle:
    print("Execution without exception")
------------------------------
Print exception information when an exception occurs“ msg"，When there are no exceptions, execute esle，Print "Execute without exception"

The use of an exception in conjunction with finallyd:

try:
    print(a)
except NameError as msg:
    print(msg)
finally:
    print("Execution regardless of exceptions finally)

User-defined exception throws raise:

class loogExcept(Exception):
    def __init__(self,leng):
        self.leng = leng

    def __str__(self):
        print("Your Name:"+str(self.leng)+",Over the length!")

def name_Test():
    try:
        name = input("enter your name:")
        if len(name) > 4:
            raise loogExcept(len(name))
        else:
            print(name)
    except loogExcept as e_result:
        print("Anomalies caught")
        print("Print exception:",e_result)

if __name__ == "__main__":
    name_Test()
---------------------------------------------

enter your name:sadsadasd
Anomalies caught
Print exception: your name: 9,Over the length!
Your name: 9,Over the length!
Traceback (most recent call last):
File "D:/project1/test.py", line 19, in name_Test
raise loogExcept(len(name))
__main__.loogExcept: <exception str() failed>

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
File "D:/project1/test.py", line 27, in <module>
name_Test()
File "D:/project1/test.py", line 24, in name_Test
print("Print exception:",e_result)
TypeError: __str__ returned non-string (type NoneType)

Process finished with exit code 1